High-frequency induction furnace



Jan. 19, 1943. H. J. M. VAN EMBDEN 2,308,945

HIGH FREQUENCY INDUCTION FURNACE Filed May 2, 1940 Patented Jan. 19, 1943 HIGH-FREQUENCY INDUCTION FURNACE Hendrik Johannes 'Meerkamp van Embden, Eindhoven, Netherlands, assignor, by mesne assignments, to Hartford National Bank and Trust Company, Hartford, Conn, as trustee Application May 2, 1940, Serial No. 333,022 In Germany May 5, 1939 3 Claims.

This invention relates to a high-frequency induction furnace, for heattreatment of materials in vacuo, provided with an energising coil for the obtainment of the high-frequency induction field in the furnace charge.

A desideratum of such furnaces is that the furnace wall, which is heated by heat radiation from the charge, should always be vacuum-tight. since it is impossible for the exciting coil to be enclosed in the vacuum space itself, in which event there is the risk that flashing-over between the windings may occur, it must be arranged outside the furnace wall. However, this arrangement involves the necessity of making the furnace wall of non-conducting material which should also be refractory and gas-tight. in the well-known construction these desiderata can only be obtained with difficulty. Generally, walls of ceramic material, such as chamotte, china or the like are used. Walls of comparatively large size when made of these materials can, however, only be handled with diilicuity since they are very sensitive to shocks and temperature changes.

The invention offers a satisfactory solution to all the problems mentioned above and resides in the use of the exciting coil for the induction field to serve at least partly as the furnace wall.

Since the exciting coil is itself necessarily made of metal, preferably of copper, the condition of vacuum-tightness is satisfied even at comparatively high temperatures and there is in addition no danger that breakage due to shocks or temperature changes may occur. In addition, the construction of the furnace is simpliiied since for one part of the wall which entails the greatest difficulties the sensitive ceramic material is replaced by metal, heat insulation of ceramic material may be provided between the crucible and the furnace wall, but need not be vacuum-tight so that the materials used need not satisfy high requirements.

The furnace wall according to the invention may be constituted either of a plurality of turns or of a single turn. Between the turns or the ends of the turns there must be a vacuum-tight but insulating connection. This connection, which may be limited to a narrow strip only is, however, bounded on either side by metal so that it can be readily cooled artificially and thus be handled more satisfactorily.

In order that the invention ,may be clearly understood and readily carried into effect it will now be described more fully with reference to iii the accompanying drawing in which two constructional examples are illustrated.

Fig. 1 is a longitudinal section of one furnace.

Fig. 2 a cross sectional view at the top of the induction coil.

Fig. 3 shows a further form of construction of theinduction coil.

Referringto the figures, reference numeral i designates the crucible pot which is carried on a stone base 3 by means of a support 32 of ceramic material. This base is provided with a surface-ground edge 4 on which, with the interposition of a packing 5, the lower surface of a hollow copper coil 8, which is also machined flat, is fitted in a vacuum-tight manner. The connection of an insulating, for example china, intermediate ring I to the upper surface of the coil 8 and a copper hood 8 is similarly established. This intermediate ring i only serves to maintain the high frequency field away from the metal hood 8.. Even a comparatively narrow ring having a width of about 20 cms. suffices so that there is little danger that this ring will crack due to uneven heating. Besides, this ring I is outside the zone of highest temperatures. The intermediate space between the crucible pot i and the furnace wall 8 may be filled with ceramic material ill for the purpose of heat insulation. For connection to the vacuum pump the hood ilis provided with atubular projection 9.

To excite the high-frequency field use is made in the usual way of a multi-electrode discharge tube or a motor generator coupled to a tuned oscillatory circuit. The exciting coil 8 of the furnace constitutes the inductance of this circult; a condenser battery i2 is connected in parallel with the coil. If this coil, which also constitutes the furnace wall, comprises one turn, as is shown in Fig. 2, the entire voltage is set up in the circuit between the neighbouring 'coilends separated by a thin insulating layer H and this may lead to flashing-over. By suitable proportioning of the coil and the condenser battery the voltage at the coil ends may be reduced without reducing the energy supplied. In some cases the tuned circuit has to be electrically matched to the generator. For the purpose of artificial cooling of the coil the latter is constructed as a hollow body. This hollow space has circulating in it a stream of cooling water which is introduced through an opening it and discharged by means of an opening it.

In the form of construction shown in Fig. 3' the coil is divided into two half-turns ii and It and the two neighbouring ends of each halfturn are electrically connected by half the condenser battery 23 and 24 respectively. In addition, there is only half the circuit voltage between each two neighbouring ends of the coil so that the insulating layers l1 and- It may be thinner and can be cooled more emciently.

Each of the half-turns constitutes a closed hollow body which has cooling-liquid flowing through it. Each of the halt-turns is therefore provided with an inlet opening ll, 22 and an outlet opening 20, 2 I. The cooling water is thus compelled to pass through each half-tum from one end to the other. For the circulation of water inside the bodies II and I! provision may be made of guide ribs or baflies.

What I claim is:

1. A high frequency inductance furnace for the treatment of material under vacuum. comprising a container for holding the material to be treated, a vacuum-tight enclosure surrounding said container and including a metal mem ber provided with an axial slit and acting as a single turn winding, insulating material within said slit and forming a vacuum-tight joint, and means to produce high-frequency heating current within the material to be treated including a tuned oscillatory circuit, said circuit comprising a source of alternating voltage, a condenser and said metal member, the metal member acting as the sole inductance of the circuit.

2. A high frequency inductance furnace for aaoaace the treatment of material under vacuum, comprising a container for holding the material to be treated. a vacuum-tight enclosure surrounding said container and including a plurality of metal members acting as a single turn wind ing, strips of insulating material between adiacent ends of said members and forming vacuum-tight joints. and means to produce highfrequency heating current within the material to be treated including a tuned oscillatory circuit, said circuit comprising a source of alternating voltage, a plurality of condensers and said metal members, the metal members acting as the sole inductance of the circuit.

3. A high frequency inductance furnace for the treatment of material under vacuum, comprising a container for holding the material to be treated, a vacuum-tight enclosure surrounding said container and including a cylindrical metal member provided with an axial slit and acting as a single turn winding, insulating material within said slit and forming a vacuum tight joint, and means to produce high-frequency heating current within the material to be treated including a tuned oscillatory circuit, said circuit comprising a source of alternating voltage, said metal member, and a condenser connected to the ends of said metal member, the metal member acting as the sole inductance of the circuit.

HENDRIX JOHANNES MEERKAMP van EMBDEN. 

